1. Field of the Invention
The present invention relates to a process for preparing a high 2-O-.alpha.-D-glucopyranosyl-L-ascorbic acid content product, more particularly, to a process for preparing a high 2-O-.alpha.-D-glucopyranosyl-L-ascorbic acid content from a solution containing 2-O-.alpha.-D-glucopyranosyl-L-ascorbic acid and a saccharide derivative of L-ascorbic acid exhibiting a direct reducing activity.
2. Description of the Prior Art
As disclosed in Japanese Patent Laid-Open Nos. 135,992/91 and 139,288/91, 2-O-.alpha.-D-glucopyranosyl-L-ascorbic acid is a novel saccharide derivative of L-ascorbic acid which has the chemical structure shown by the formula I, a satisfiable stability and substantial no direct reducing activity, as well as being readily hydrolyzed in vivo to exert the inherent physiological activity of L-ascorbic acid. Formula I: ##STR1##
The industrial-scale preparations of 2-O-.alpha.-D-glucopyranosyl-L-ascorbic acid are, for example, a preparation as disclosed in Japanese Patent Laid-Open No. 183,492/91 comprising allowing a solution containing an .alpha.-glucosyl saccharide and L-ascorbic acid to the action of a saccharide-transferring enzyme together with or without glucoamylase to form a solution containing 2-O-.alpha.-D-glucopyranosyl-L-ascorbic acid and other concomitants; subjecting the resultant solution as a material solution to column chromatography using a strongly-acidic cation exchange resin; and recoverying the resultant high 2-O-.alpha.-D-glucopyranosyl-L-ascorbic acid content fraction; and, if necessary, further concentrating the fraction into a supersaturated solution to obtain a crystalline 2-O-.alpha.-D-glucopyranosyl-L-ascorbic acid.
During the study of a preparation of a high 2-O-.alpha.-D-glucopyranosyl-L-ascorbic acid content product, the present inventors found that a solution containing 2-O-.alpha.-D-glucopyranosyl-L-ascorbic acid and other concomitants as a material solution had a drawback in the step of column chromatography using a strongly-acidic cation exchange resin, i.e. there coexisted in such a material solution concomitants such as L-ascorbic acid and glucose which were separable with a relative easiness from 2-O-.alpha.-D-glucopyranosyl-L-ascorbic acid, and relatively-small amounts of unknown substances which substantially could not be separated from 2-O-.alpha.-D-gluco-pyranosyl-L-ascorbic acid and hindered the increment of the purity of a high 2-O-.alpha.-D-glucopyranosyl-L-ascorbic acid content fraction, as well as inhibiting the crystallization of 2-O-.alpha.-D-glucopyranosyl-L-ascorbic acid in its supersaturated solution.
The present inventors also found that the unknown substances, which were accumulated in a mother liquor in which a crystalline 2-O-.alpha.-D-glucopyranosyl-L-ascorbic acid had been removed, inhibited the crystallization of 2-O-.alpha.-D-gluco-pyranosyl-L-ascorbic acid in the mother liquor, and strongly lowered the yield of the crystal in the second- and third-crystallization steps.
It has been a great demand to reveal unknown substances coexisted in a solution of 2-O-.alpha.-D-glucopyranosyl-L-ascorbic acid prepared by a saccharide-transfer reaction, and to establish an industrial-scale preparation of a high-purity 2-O-.alpha.-D-glucopyranosyl-L-ascorbic acid in a relatively-high yield by removing concomitants with a relative easiness from a solution containing the concomitants and 2-O-.alpha.-D-gluco-pyranosyl-L-ascorbic acid.